WO2021220887A1 - Elastic wave device - Google Patents

Elastic wave device Download PDF

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Publication number
WO2021220887A1
WO2021220887A1 PCT/JP2021/016046 JP2021016046W WO2021220887A1 WO 2021220887 A1 WO2021220887 A1 WO 2021220887A1 JP 2021016046 W JP2021016046 W JP 2021016046W WO 2021220887 A1 WO2021220887 A1 WO 2021220887A1
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layer
elastic wave
piezoelectric
film
electrode
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PCT/JP2021/016046
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French (fr)
Japanese (ja)
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克也 大門
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株式会社村田製作所
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Priority to CN202180029093.9A priority Critical patent/CN115428333A/en
Priority to KR1020227037096A priority patent/KR20220158788A/en
Publication of WO2021220887A1 publication Critical patent/WO2021220887A1/en
Priority to US17/969,730 priority patent/US20230037955A1/en

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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/125—Driving means, e.g. electrodes, coils
    • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
    • H03H9/14538—Formation
    • H03H9/14541—Multilayer finger or busbar electrode
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/125—Driving means, e.g. electrodes, coils
    • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02007—Details of bulk acoustic wave devices
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02535—Details of surface acoustic wave devices
    • H03H9/02543—Characteristics of substrate, e.g. cutting angles
    • H03H9/02574—Characteristics of substrate, e.g. cutting angles of combined substrates, multilayered substrates, piezoelectrical layers on not-piezoelectrical substrate
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02535—Details of surface acoustic wave devices
    • H03H9/02818—Means for compensation or elimination of undesirable effects
    • H03H9/02842—Means for compensation or elimination of undesirable effects of reflections
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02535—Details of surface acoustic wave devices
    • H03H9/02818—Means for compensation or elimination of undesirable effects
    • H03H9/02858—Means for compensation or elimination of undesirable effects of wave front distortion
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02535—Details of surface acoustic wave devices
    • H03H9/02818—Means for compensation or elimination of undesirable effects
    • H03H9/02881—Means for compensation or elimination of undesirable effects of diffraction of wave beam
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02535—Details of surface acoustic wave devices
    • H03H9/02992—Details of bus bars, contact pads or other electrical connections for finger electrodes
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/125—Driving means, e.g. electrodes, coils
    • H03H9/13—Driving means, e.g. electrodes, coils for networks consisting of piezoelectric or electrostrictive materials
    • H03H9/131—Driving means, e.g. electrodes, coils for networks consisting of piezoelectric or electrostrictive materials consisting of a multilayered structure
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/25—Constructional features of resonators using surface acoustic waves

Definitions

  • the present invention relates to an elastic wave device.
  • Patent Document 1 discloses an example of an elastic wave device.
  • an IDT (Interdigital Transducer) electrode is provided on the piezoelectric layer.
  • a plurality of dielectric films are provided between the tips of the plurality of electrode fingers of the IDT electrode and the piezoelectric layer.
  • the dielectric used for the dielectric film include SiO 2 , Al 2 O 3 , PSG (phosphoric acid glass) and BSG (borosilicate glass).
  • An object of the present invention is to provide an elastic wave device capable of suppressing the transverse mode more reliably.
  • a piezoelectric substrate and an IDT electrode provided on the piezoelectric substrate and having a plurality of electrode fingers are provided, and the IDT electrodes are adjacent to each other.
  • the portion where the electrode fingers overlap in the elastic wave propagation direction is a crossing region, and the crossing region is a central region located on the central side in the direction in which the plurality of electrode fingers extend, and the plurality of the central regions. It has a pair of edge regions arranged on both sides in the direction in which the electrode fingers extend, and in the pair of edge regions, a dielectric film provided between the piezoelectric substrate and the plurality of electrode fingers is further formed.
  • the dielectric film comprises at least one dielectric selected from the group consisting of hafnium oxide, niobium oxide, tungsten oxide and cerium oxide.
  • a piezoelectric substrate having a piezoelectric layer and an IDT electrode provided on the piezoelectric substrate and having a plurality of electrode fingers are provided.
  • the portion where the adjacent electrode fingers of the IDT electrode overlap in the elastic wave propagation direction is a crossing region, and the crossing region is a central region located on the central side in the direction in which the plurality of electrode fingers extend, and the above. It has a pair of edge regions arranged on both sides in a direction in which the plurality of electrode fingers extend in a central region, and is provided between the piezoelectric substrate and the plurality of electrode fingers in the pair of edge regions.
  • the piezoelectric film is further provided, the piezoelectric layer is a lithium tantalate layer, the IDT electrode has a main electrode layer, the main electrode layer is an Al layer, and the electrode finger of the IDT electrode.
  • the wavelength defined by the pitch is ⁇ [ ⁇ m]
  • the thickness of the dielectric film is t_D [ ⁇ ]
  • the dielectric constant of the dielectric film is ⁇
  • the density of the dielectric film is d [kg / m 3 ]
  • the Young ratio of the dielectric film is Y [GPa]
  • the thickness of the piezoelectric layer is t_LT [ ⁇ ]
  • the thickness of the main electrode layer of the IDT electrode is t_Al [ ⁇ ]
  • the sound velocity in the central region is Vc, and the above.
  • the t_D [ ⁇ ] When the sound velocity in the pair of edge regions is Ve, the t_D [ ⁇ ], the ⁇ , the d [kg / m 3 ], the Y [GPa], the t_LT [ ⁇ ], and the t_Al [ ⁇ ] are It is a value at which Ve / Vc derived by the following equation 1 is less than 1.
  • the transverse mode can be suppressed more reliably.
  • FIG. 1 is a front sectional view of an elastic wave device according to a first embodiment of the present invention.
  • FIG. 2 is a plan view of the elastic wave device according to the first embodiment of the present invention.
  • FIG. 3 is a diagram showing the relationship between the thickness of the dielectric film and the speed of sound in the elastic wave device of the first comparative example and the reference example.
  • FIG. 4 is a diagram showing the relationship between the thickness of the dielectric film and the speed of sound in the elastic wave device according to the first embodiment of the present invention.
  • FIG. 5 is a diagram showing impedance frequency characteristics according to the first embodiment of the present invention.
  • FIG. 6 is a diagram showing impedance frequency characteristics in the second comparative example.
  • FIG. 7 is a front sectional view of an elastic wave device according to a first modification of the first embodiment of the present invention.
  • FIG. 8 is a front sectional view of an elastic wave device according to a second modification of the first embodiment of the present invention.
  • FIG. 9 is a front sectional view of an elastic wave device according to a third modification of the first embodiment of the present invention.
  • FIG. 10 is a front sectional view of an elastic wave device according to a fourth modification of the first embodiment of the present invention.
  • FIG. 11 is a front sectional view of the elastic wave device according to the second embodiment of the present invention.
  • FIG. 1 is a front sectional view of an elastic wave device according to a first embodiment of the present invention.
  • FIG. 2 is a plan view of the elastic wave device according to the first embodiment. Note that FIG. 1 is a cross-sectional view passing through the line II in FIG. 2, and is a cross-sectional view passing through the first edge region described later.
  • the elastic wave device 1 shown in FIGS. 1 and 2 the transverse mode is suppressed by establishing the piston mode.
  • the elastic wave device 1 has a piezoelectric substrate 2.
  • An IDT electrode 7 is provided on the piezoelectric substrate 2.
  • the IDT electrode 7 has a plurality of electrode fingers.
  • a dielectric film 15A and a dielectric film 15B are provided between the tips of the plurality of electrode fingers and the piezoelectric substrate 2.
  • the dielectric film 15A and the dielectric film 15B are composed of at least one dielectric selected from the group consisting of hafnium oxide, niobium oxide, tungsten oxide and cerium oxide.
  • the piezoelectric substrate 2 has a support substrate 3, a hypersonic film 4 as a hypersonic material layer, a low sound velocity film 5, and a piezoelectric layer 6. More specifically, the hypersonic film 4 is provided on the support substrate 3. A low sound velocity film 5 is provided on the high sound velocity film 4. The piezoelectric layer 6 is provided on the bass velocity film 5.
  • An IDT electrode 7 is provided on the piezoelectric layer 6 of the piezoelectric substrate 2. By applying an AC voltage to the IDT electrode 7, elastic waves are excited. As shown in FIG. 2, a pair of reflectors 8 and reflectors 9 are provided on both sides of the IDT electrode 7 in the elastic wave propagation direction on the piezoelectric substrate 2.
  • the elastic wave device 1 is an elastic surface wave resonator.
  • the elastic wave device according to the present invention is not limited to the elastic wave resonator, and may be a filter device or a multiplexer having an elastic wave resonator.
  • the IDT electrode 7 has a first bus bar 16, a second bus bar 17, a plurality of first electrode fingers 18, and a plurality of second electrode fingers 19.
  • the first bus bar 16 and the second bus bar 17 face each other.
  • One end of each of the plurality of first electrode fingers 18 is connected to the first bus bar 16.
  • One end of each of the plurality of second electrode fingers 19 is connected to the second bus bar 17.
  • the plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are interleaved with each other.
  • the elastic wave propagation direction is defined as the x direction.
  • the direction in which the first electrode finger 18 and the second electrode finger 19 extend is defined as the first direction y.
  • the x-direction and the y-direction are orthogonal to each other.
  • the IDT electrode 7 has a main electrode layer and two adhesion layers. From the piezoelectric layer 6 side, the adhesion layer, the main electrode layer, and the adhesion layer are laminated in this order.
  • the main electrode layer is the dominant electrode layer in the excitation of elastic waves.
  • the two close contact layers are both Ti layers, and the main electrode layer is an Al layer.
  • the material of the IDT electrode 7 is not limited to the above. Alternatively, the IDT electrode 7 may consist only of the main electrode layer. The same material as the IDT electrode 7 can be used for the reflector 8 and the reflector 9.
  • the piezoelectric layer 6 is a lithium tantalate layer. More specifically, the piezoelectric material used in the piezoelectric layer 6 is 55 ° Y-cut X propagation LiTaO 3 . The material and cut angle of the piezoelectric layer 6 are not limited to the above.
  • the low sound velocity film 5 is a relatively low sound velocity film. More specifically, the sound velocity of the bulk wave propagating in the bass velocity film 5 is lower than the sound velocity of the bulk wave propagating in the piezoelectric layer 6.
  • the bass velocity film 5 of the present embodiment is a silicon oxide film. Silicon oxide is represented by SiO a. a is an arbitrary positive number. The silicon oxide constituting the bass velocity film 5 of the present embodiment is SiO 2 .
  • the material of the bass velocity film 5 is not limited to the above, and is, for example, a material containing glass, silicon nitride, lithium oxide, tantalum pentoxide, or a compound obtained by adding fluorine, carbon, or boron to silicon oxide as a main component. Can also be used.
  • the hypersonic material layer is the hypersonic film 4.
  • the hypersonic material layer is a relatively hypersonic layer. More specifically, the sound velocity of the bulk wave propagating in the hypersonic material layer is higher than the sound velocity of the elastic wave propagating in the piezoelectric layer 6.
  • the hypersonic film 4 as the hypersonic material layer is a silicon nitride film.
  • the silicon nitride constituting the hypersonic film 4 of the present embodiment is SiN.
  • the material of the treble velocity film 4 is not limited to the above, and for example, silicon, aluminum oxide, silicon carbide, silicon nitride, sapphire, lithium tantalate, lithium niobate, crystal, alumina, zirconia, cordierite, mulite, etc.
  • a medium containing the above materials as a main component such as steatite, forsterite, magnesia, DLC (diamond-like carbon) film, or diamond, can also be used.
  • the support substrate 3 is a silicon substrate.
  • the material of the support substrate 3 is not limited to the above, and for example, piezoelectric materials such as aluminum oxide, lithium tantalate, lithium niobate, and crystal, alumina, sapphire, magnesia, silicon nitride, aluminum nitride, silicon carbide, zirconia, and the like.
  • Various ceramics such as cozilite, mulite, steatite, and forsterite, dielectrics such as diamond and glass, semiconductors or resins such as gallium nitride can also be used.
  • the piezoelectric substrate 2 has a structure in which the hypersonic film 4, the hypersonic film 5 and the piezoelectric layer 6 as the hypersonic material layer are laminated in this order. Thereby, the energy of the elastic wave can be effectively confined on the piezoelectric layer 6 side.
  • the crossing region A has a central region C, a first edge region E1 and a second edge region E2.
  • the central region C is located on the central side in the y direction in the crossing region A.
  • the first edge region E1 and the second edge region E2 are arranged on both sides of the central region C in the y direction. More specifically, the first edge region E1 is arranged on the first bus bar 16 side of the central region C.
  • the second edge region E2 is arranged on the second bus bar 17 side of the central region C.
  • the first edge region E1 and the second edge region E2 may be simply referred to as an edge region.
  • the IDT electrode 7 has a first gap region G1 and a second gap region G2.
  • the first gap region G1 is located between the first edge region E1 and the first bus bar 16.
  • the second gap region G2 is located between the second edge region E2 and the second bus bar 17.
  • the first gap region G1 only the first electrode finger 18 of the first electrode finger 18 and the second electrode finger 19 is provided.
  • the speed of sound in the first gap region G1 is higher than the speed of sound in the central region C.
  • the second gap region G2 only the second electrode finger 19 of the first electrode finger 18 and the second electrode finger 19 is provided.
  • the speed of sound in the second gap region G2 is higher than the speed of sound in the central region C.
  • the high sound velocity region is configured in the first gap region G1 and the second gap region G2.
  • one dielectric film 15A is provided between the piezoelectric substrate 2, all the first electrode fingers 18, and all the second electrode fingers 19. There is.
  • the dielectric film 15A has a band-like shape.
  • the dielectric film 15A is also provided on the piezoelectric substrate 2 between all the electrode fingers. Further, the dielectric film 15A is also provided between the piezoelectric substrate 2 and the reflector 8 and the reflector 9.
  • one dielectric film 15B is provided between the piezoelectric substrate 2 and all the first electrode fingers 18 and all the second electrode fingers 19. There is.
  • the dielectric film 15B has a band-like shape.
  • the dielectric film 15B is also provided on the piezoelectric substrate 2 between all the electrode fingers.
  • the dielectric film 15B is also provided between the piezoelectric substrate 2 and the reflector 8 and the reflector 9.
  • the dielectric film 15A and the dielectric film 15B do not have to be provided between the piezoelectric substrate 2 and the reflector 8 and the reflector 9.
  • the configuration is not limited to the configuration in which one dielectric film 15A is provided between the piezoelectric substrate 2 and all the electrode fingers of the IDT electrode 7.
  • the elastic wave device 1 may have a plurality of dielectric films 15A.
  • the dielectric film 15A may be provided between the piezoelectric substrate 2 and at least one electrode finger of the IDT electrode 7.
  • the dielectric film 15A does not have to be provided in the portion between the plurality of electrode fingers on the piezoelectric substrate 2.
  • it is preferable that the dielectric films 15A are provided between the piezoelectric substrate 2 and all the electrode fingers.
  • the elastic wave device 1 may have a plurality of dielectric films 15B.
  • the dielectric film 15B may be provided between the piezoelectric substrate 2 and at least one electrode finger of the IDT electrode 7.
  • the dielectric film 15B does not have to be provided in the portion between the plurality of electrode fingers on the piezoelectric substrate 2.
  • the dielectric film 15A and the dielectric film 15B are made of at least one dielectric selected from the group consisting of hafnium oxide, niobium oxide, tungsten oxide and cerium oxide.
  • the speed of sound in the first edge region E1 and the second edge region E2 is Ve
  • Ve ⁇ Vc can be set.
  • the bass sound region is more reliably configured in the first edge region E1 and the second edge region E2.
  • the details of the effect that can be Ve ⁇ Vc, that is, Ve / Vc ⁇ 1 are shown below.
  • the behavior of changes in sound velocity was compared in the elastic wave device having the configuration of the first embodiment, the first comparative example, and the reference example. More specifically, the behavior of the change in sound velocity with respect to the change in the film thickness of the dielectric film was compared.
  • the behavior of the speed of sound was investigated in each of the cases where the dielectric film was an HfO 2 film, an Nb 2 O 5 film, a WO 3 film, and a CeO 2 film.
  • the dielectric used for the dielectric film is different from that of the first embodiment.
  • the behavior of the speed of sound was investigated in each of the cases where the dielectric film was a SiO 2 film and a SiN film.
  • the reference example differs from the first embodiment in that the dielectric film is provided on the IDT electrode and the dielectric film is the SiO 2 film. The speed of sound was measured even when the dielectric film was not provided.
  • the design parameters of the elastic wave device having the configuration of the first embodiment and the elastic wave device of the first comparative example and the reference example are as follows.
  • Support substrate Material ... Si Hypersonic film; Material: SiN, Thickness: 300 nm Bass velocity film; Material: SiO 2 , Thickness: 300 nm Piezoelectric layer; Material: 55 ° Y-cut X propagation LiTaO 3 , Thickness: 400 nm
  • Layer structure of IDT electrode Layer structure: Ti layer / Al layer / Ti layer from the piezoelectric layer side, thickness: 12 nm / 100 nm / 4 nm from the piezoelectric layer side IDT electrode wavelength; 2 ⁇ m IDT electrode duty ratio; 0.5 Dielectric film; Thickness: 5 nm or more, 65 nm or less, or 5 nm or more, 55 nm or less, changed in 10 nm increments.
  • FIG. 3 is a diagram showing the relationship between the thickness of the dielectric film and the speed of sound in the elastic wave device of the first comparative example and the reference example.
  • FIG. 4 is a diagram showing the relationship between the thickness of the dielectric film and the speed of sound in the elastic wave device according to the first embodiment.
  • the speed of sound is higher than when the dielectric film is not provided. Further, the thicker the dielectric film, the higher the speed of sound. Similarly, when the dielectric film is a SiN film, the thicker the dielectric film, the higher the speed of sound. Even if the dielectric film is a SiO 2 film as in the reference example, when the dielectric film is provided on the IDT electrode, the thicker the dielectric film, the lower the speed of sound.
  • the dielectric film 15A and the dielectric film 15B are the HfO 2 film, the Nb 2 O 5 film, the WO 3 film, and the CeO 2 film. It can be seen that the thicker the dielectric film 15A and the dielectric film 15B, the lower the sound velocity. As described above, in the first embodiment, the low sound velocity region can be more reliably configured in the first edge region E1 and the second edge region E2.
  • the low sound velocity region can be more reliably arranged outside the central region C in the y direction. Further, the high sound velocity region is located outside the low sound velocity region. Therefore, the piston mode can be established more reliably. Therefore, the transverse mode can be suppressed more reliably.
  • the present inventor has found that the suppression of the transverse mode depends on the dielectric constants of the dielectric film 15A and the dielectric film 15B. The details will be described below.
  • the impedance frequency characteristics were compared by simulation.
  • an HfO 2 film was used as the dielectric film.
  • the elastic constant and density of the dielectric film were defined as the elastic constant and density of the HfO 2 film
  • the dielectric constant of the dielectric film was defined as the dielectric constant of the SiO 2 film.
  • the design parameters of the elastic wave device having the configuration of the first embodiment and the elastic wave device of the second comparative example are the same as in the case of comparing the behavior of the sound velocity except for the thickness of the dielectric film.
  • the thickness of the dielectric film was 30 nm.
  • FIG. 5 is a diagram showing impedance frequency characteristics in the first embodiment.
  • FIG. 6 is a diagram showing impedance frequency characteristics in the second comparative example.
  • the transverse mode is suppressed.
  • the arrow B in FIG. 6 in the second comparative example, a large spurious due to the transverse mode is generated.
  • the elastic constant and density of the dielectric film are the same as the elastic constant and density of the HfO 2 film, if the dielectric constant of the dielectric film is the same as the dielectric constant of the SiO 2 film, it is difficult to suppress the transverse mode. I understand. As described above, it can be seen that the suppression of the transverse mode depends on the dielectric constant of the dielectric film.
  • ⁇ be the wavelength defined by the electrode finger pitch of the IDT electrode.
  • the electrode finger pitch refers to the distance between the center of the electrode fingers in the adjacent electrode fingers. Specifically, it refers to the distance connecting the center points in the x direction of each of the adjacent electrode fingers.
  • the electrode finger pitch is assumed to be the average value of the distances between the center of the electrode fingers.
  • the thickness of the dielectric film is t_D [ ⁇ ]
  • the dielectric constant of the dielectric film is ⁇
  • the density of the dielectric film is d [kg / m 3 ]
  • the Young ratio of the dielectric film is Y [GPa]
  • the piezoelectric material is the thickness of the dielectric film.
  • the thickness of the layer is t_LT [ ⁇ ]
  • the thickness of the main electrode layer of the IDT electrode is t_Al [ ⁇ ]
  • the speed of sound in the central region is Vc
  • the speed of sound in the pair of edge regions is Ve.
  • Ve / Vc was calculated under each condition by changing each of the above parameters.
  • the design parameters of the elastic wave device are as follows. In the following, the unit of each of the above parameters may be omitted.
  • Support substrate Material ... Si Hypersonic film; Material: SiN, Thickness: 300 nm Bass velocity film; Material: SiO 2 , Thickness: 300 nm Piezoelectric layer; Material: 55 ° Y-cut X propagation LiTaO 3 , Thickness: t_LT Layer structure of IDT electrode; Layer structure: Ti layer / Al layer / Ti layer from the piezoelectric layer side, thickness: 12 nm / t_Al / 4 nm from the piezoelectric layer side IDT electrode wavelength; 2 ⁇ m IDT electrode duty ratio; 0.5 The density of the dielectric film d; 2kg / m 3 or more, in 8 kg / m 3 or less of the range was varied 2 kg / m 3 increments.
  • the Young's modulus of the dielectric film was changed in 70 GPa increments in the range of 70 GPa or more and 280 GPa or less.
  • the dielectric constant of the dielectric film was changed in increments of 5 in the range of ⁇ ; 5 or more and 35 or less.
  • the thickness of the dielectric film t_D was changed in 0.0025 ⁇ increments in the range of 0.0025 ⁇ or more and 0.0175 ⁇ or less.
  • the thickness of the piezoelectric layer t_LT was changed in 0.05 ⁇ increments in the range of 0.15 ⁇ or more and 0.3 ⁇ or less.
  • the thickness of the Al layer t_Al was changed in 0.0125 ⁇ increments in the range of 0.05 ⁇ or more and 0.075 ⁇ or less.
  • t_D [ ⁇ ], ⁇ , d [kg / m 3 ], Y [GPa], t_LT [ ⁇ ] and t_Al [ ⁇ ] may be values such that Ve / Vc derived by Equation 1 is less than 1. .. Thereby, the pair of edge regions can be surely set as the low sound velocity region. As a result, the piston mode can be established and the transverse mode can be suppressed.
  • the dielectric film 15A and the dielectric film 15B shown in FIG. 2 are composed of hafnium oxide, niobium oxide, and oxidation. It does not have to contain tungsten and cerium oxide. However, it is preferable that the dielectric film 15A and the dielectric film 15B are made of at least one dielectric selected from the group consisting of hafnium oxide, niobium oxide, tungsten oxide and cerium oxide.
  • the piezoelectric layer 6 is indirectly provided on the hypersonic film 4 via the hypersonic film 5.
  • the configuration of the piezoelectric substrate 2 is not limited to the above.
  • first to third modifications of the first embodiment in which only the configuration of the piezoelectric substrate is different from that of the first embodiment, will be shown.
  • the transverse mode can be suppressed more reliably as in the first embodiment.
  • the energy of elastic waves can be effectively confined to the piezoelectric layer 6 side.
  • the piezoelectric substrate 22A has a support substrate 3, a hypersonic film 4, and a piezoelectric layer 6.
  • the piezoelectric layer 6 is directly provided on the hypersonic film 4 as the hypersonic material layer.
  • the hypersonic material layer is the hypersonic support substrate 24.
  • the piezoelectric substrate 22B has a hypersonic support substrate 24, a low sound velocity film 5, and a piezoelectric layer 6.
  • the hypersonic film 5 is provided on the hypersonic support substrate 24.
  • Examples of the material of the high-pitched sound support substrate 24 include aluminum oxide, silicon carbide, silicon nitride, silicon nitride, silicon, sapphire, lithium tantrate, lithium niobate, crystal, alumina, zirconia, cordierite, mulite, and steatite. , Forsterite, magnesia, DLC film, diamond, or the like, or a medium containing the above-mentioned material as a main component can be used.
  • the piezoelectric substrate 22C has a hypersonic support substrate 24 and a piezoelectric layer 6.
  • the piezoelectric layer 6 is directly provided on the hypersonic support substrate 24 as the hypersonic material layer.
  • the piezoelectric substrate 22D is composed of only the piezoelectric layer.
  • the piezoelectric substrate 22D is a piezoelectric substrate.
  • the transverse mode can be suppressed more reliably, as in the first embodiment.
  • FIG. 11 is a front sectional view of the elastic wave device according to the second embodiment.
  • the piezoelectric substrate 32 has an acoustic reflection film 37. More specifically, the piezoelectric substrate 32 has a support substrate 3, an acoustic reflection film 37, and a piezoelectric layer 6. An acoustic reflection film 37 is provided on the support substrate 3. The piezoelectric layer 6 is provided on the acoustic reflection film 37. Except for the above points, the elastic wave device 31 of the present embodiment has the same configuration as the elastic wave device 1 of the first embodiment.
  • the acoustic reflection film 37 is a laminate of a plurality of acoustic impedance layers. More specifically, the acoustic reflection film 37 has a plurality of low acoustic impedance layers and a plurality of high acoustic impedance layers.
  • the low acoustic impedance layer is a layer having a relatively low acoustic impedance.
  • the plurality of low acoustic impedance layers of the acoustic reflection film 37 are a low acoustic impedance layer 35a and a low acoustic impedance layer 35b.
  • the high acoustic impedance layer is a layer having a relatively high acoustic impedance.
  • the plurality of high acoustic impedance layers of the acoustic reflection film 37 are a high acoustic impedance layer 34a and a high acoustic impedance layer 34b.
  • the low acoustic impedance layer and the high acoustic impedance layer are alternately laminated.
  • the low acoustic impedance layer 35a is a layer located closest to the piezoelectric layer 6 in the acoustic reflection film 37.
  • the acoustic reflection film 37 has two layers each of a low acoustic impedance layer and a high acoustic impedance layer. However, the acoustic reflection film 37 may have at least one low acoustic impedance layer and one high acoustic impedance layer.
  • the material of the low acoustic impedance layer for example, silicon oxide or aluminum can be used.
  • a metal such as platinum or tungsten or a dielectric material such as aluminum nitride or silicon nitride can be used.
  • the elastic wave device 31 Since the elastic wave device 31 has the acoustic reflection film 37, the energy of the elastic wave can be effectively confined to the piezoelectric layer 6 side.
  • the electrode structure on the piezoelectric substrate 32 in this embodiment is the same as that in the first embodiment. Therefore, the speed of sound can be more reliably lowered in the pair of edge regions, and the piston mode can be more reliably established. Therefore, the transverse mode can be suppressed more reliably.

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Abstract

The present invention provides an elastic wave device that enables more reliable transverse mode suppression.　An elastic wave device 1 according to the present invention comprises: a piezoelectric substrate 2; and an IDT electrode 7 that is provided upon the piezoelectric substrate 2 and has a plurality of electrode fingers. A section where adjacent electrode fingers of the IDT electrode 7 overlap in the elastic wave propagation direction is designated as a crossover region A. The crossover region A includes: a center region C that is positioned toward the center in the direction in which the plurality of electrode fingers extend; and first and second edge regions E1, E2 that are respectively disposed on both sides of the center region C in the direction in which the plurality of electrode fingers extend. The elastic wave device 1 further comprises, in the respective first and second edge regions E1, E2, dielectric films 15A, 15B that are provided between the piezoelectric substrate 2 and the plurality of electrode fingers. The dielectric films 15A, 15B are formed from at least one dielectric selected from the group consisting of hafnium oxides, niobium oxides, tungsten oxides, and cerium oxides.

Description

弾性波装置Elastic wave device
　本発明は、弾性波装置に関する。 The present invention relates to an elastic wave device.
　従来、弾性波装置は携帯電話機のフィルタなどに広く用いられている。下記の特許文献１には、弾性波装置の一例が開示されている。この弾性波装置においては、圧電体層上にＩＤＴ（Ｉｎｔｅｒｄｉｇｉｔａｌ　Ｔｒａｎｓｄｕｃｅｒ）電極が設けられている。ＩＤＴ電極の複数の電極指の先端部と、圧電体層との間には、複数の誘電体膜が設けられている。誘電体膜に用いられる誘電体として、ＳｉＯ２、Ａｌ２Ｏ３、ＰＳＧ（リンケイ酸ガラス）及びＢＳＧ（ホウケイ酸ガラス）などが挙げられている。 Conventionally, elastic wave devices are widely used as filters for mobile phones and the like. The following Patent Document 1 discloses an example of an elastic wave device. In this elastic wave device, an IDT (Interdigital Transducer) electrode is provided on the piezoelectric layer. A plurality of dielectric films are provided between the tips of the plurality of electrode fingers of the IDT electrode and the piezoelectric layer. Examples of the dielectric used for the dielectric film include SiO 2 , Al 2 O 3 , PSG (phosphoric acid glass) and BSG (borosilicate glass).
ＵＳ　２０１７／０１５５３７３　Ａ１US 2017/0155373 A1
　従来、誘電体膜としてＳｉＯ２膜を用いると、ＳｉＯ２膜を設けた領域においては、音速は低くなると考えられてきた。これにより、ピストンモードが成立すると考えられてきた。しかしながら、ＩＤＴ電極と圧電体層との間にＳｉＯ２膜を設けた場合、音速が高くなることが、本発明者の検討により明らかとなった。そのため、ＩＤＴ電極と圧電体層との間にＳｉＯ２膜を設けても、ピストンモードは成立し難く、横モードによるスプリアスを抑制することは困難である。 Conventionally, it has been considered that when a SiO 2 film is used as a dielectric film, the speed of sound becomes low in the region where the SiO 2 film is provided. It has been thought that this establishes the piston mode. However, it has been clarified by the study of the present inventor that the speed of sound increases when the SiO 2 film is provided between the IDT electrode and the piezoelectric layer. Therefore, even if the SiO 2 film is provided between the IDT electrode and the piezoelectric layer, it is difficult to establish the piston mode, and it is difficult to suppress spurious due to the transverse mode.
　本発明の目的は、横モードをより確実に抑制することができる、弾性波装置を提供することにある。 An object of the present invention is to provide an elastic wave device capable of suppressing the transverse mode more reliably.
　本発明に係る弾性波装置のある広い局面では、圧電性基板と、前記圧電性基板上に設けられており、複数の電極指を有するＩＤＴ電極とが備えられており、前記ＩＤＴ電極の隣り合う電極指が弾性波伝搬方向において重なり合っている部分が交叉領域であり、前記交叉領域が、前記複数の電極指が延びる方向における中央側に位置している中央領域と、前記中央領域の前記複数の電極指が延びる方向両側に配置されている一対のエッジ領域とを有し、前記一対のエッジ領域において、前記圧電性基板と前記複数の電極指との間に設けられている誘電体膜がさらに備えられており、前記誘電体膜が、酸化ハフニウム、酸化ニオブ、酸化タングステン及び酸化セリウムからなる群から選択された少なくとも１種の誘電体からなる。 In a wide aspect of the elastic wave device according to the present invention, a piezoelectric substrate and an IDT electrode provided on the piezoelectric substrate and having a plurality of electrode fingers are provided, and the IDT electrodes are adjacent to each other. The portion where the electrode fingers overlap in the elastic wave propagation direction is a crossing region, and the crossing region is a central region located on the central side in the direction in which the plurality of electrode fingers extend, and the plurality of the central regions. It has a pair of edge regions arranged on both sides in the direction in which the electrode fingers extend, and in the pair of edge regions, a dielectric film provided between the piezoelectric substrate and the plurality of electrode fingers is further formed. The dielectric film comprises at least one dielectric selected from the group consisting of hafnium oxide, niobium oxide, tungsten oxide and cerium oxide.
　本発明に係る弾性波装置の他の広い局面では、圧電体層を有する圧電性基板と、前記圧電性基板上に設けられており、複数の電極指を有するＩＤＴ電極とが備えられており、前記ＩＤＴ電極の隣り合う電極指が弾性波伝搬方向において重なり合っている部分が交叉領域であり、前記交叉領域が、前記複数の電極指が延びる方向における中央側に位置している中央領域と、前記中央領域の前記複数の電極指が延びる方向両側に配置されている一対のエッジ領域とを有し、前記一対のエッジ領域において、前記圧電性基板と前記複数の電極指との間に設けられている誘電体膜がさらに備えられており、前記圧電体層がタンタル酸リチウム層であり、前記ＩＤＴ電極が主電極層を有し、前記主電極層がＡｌ層であり、前記ＩＤＴ電極の電極指ピッチにより規定される波長をλ[μｍ]、前記誘電体膜の厚みをｔ＿Ｄ［λ］、前記誘電体膜の誘電率をε、前記誘電体膜の密度をｄ［ｋｇ／ｍ３］、前記誘電体膜のヤング率をＹ［ＧＰａ］、前記圧電体層の厚みをｔ＿ＬＴ［λ］、前記ＩＤＴ電極の前記主電極層の厚みをｔ＿Ａｌ［λ］とし、前記中央領域における音速をＶｃ、前記一対のエッジ領域における音速をＶｅとしたときに、前記ｔ＿Ｄ［λ］、前記ε、前記ｄ［ｋｇ／ｍ３］、前記Ｙ［ＧＰａ］、前記ｔ＿ＬＴ［λ］及び前記ｔ＿Ａｌ［λ］が、下記の式１により導出されるＶｅ／Ｖｃが１未満となる値である。 In another broad aspect of the elastic wave apparatus according to the present invention, a piezoelectric substrate having a piezoelectric layer and an IDT electrode provided on the piezoelectric substrate and having a plurality of electrode fingers are provided. The portion where the adjacent electrode fingers of the IDT electrode overlap in the elastic wave propagation direction is a crossing region, and the crossing region is a central region located on the central side in the direction in which the plurality of electrode fingers extend, and the above. It has a pair of edge regions arranged on both sides in a direction in which the plurality of electrode fingers extend in a central region, and is provided between the piezoelectric substrate and the plurality of electrode fingers in the pair of edge regions. The piezoelectric film is further provided, the piezoelectric layer is a lithium tantalate layer, the IDT electrode has a main electrode layer, the main electrode layer is an Al layer, and the electrode finger of the IDT electrode. The wavelength defined by the pitch is λ [μm], the thickness of the dielectric film is t_D [λ], the dielectric constant of the dielectric film is ε, the density of the dielectric film is d [kg / m 3 ], and the above. The Young ratio of the dielectric film is Y [GPa], the thickness of the piezoelectric layer is t_LT [λ], the thickness of the main electrode layer of the IDT electrode is t_Al [λ], the sound velocity in the central region is Vc, and the above. When the sound velocity in the pair of edge regions is Ve, the t_D [λ], the ε, the d [kg / m 3 ], the Y [GPa], the t_LT [λ], and the t_Al [λ] are It is a value at which Ve / Vc derived by the following equation 1 is less than 1.
Figure JPOXMLDOC01-appb-M000002
Figure JPOXMLDOC01-appb-M000002
　本発明に係る弾性波装置によれば、横モードをより確実に抑制することができる。 According to the elastic wave device according to the present invention, the transverse mode can be suppressed more reliably.
図１は、本発明の第１の実施形態に係る弾性波装置の正面断面図である。FIG. 1 is a front sectional view of an elastic wave device according to a first embodiment of the present invention. 図２は、本発明の第１の実施形態に係る弾性波装置の平面図である。FIG. 2 is a plan view of the elastic wave device according to the first embodiment of the present invention. 図３は、第１の比較例及び参考例の弾性波装置における、誘電体膜の厚みと音速との関係を示す図である。FIG. 3 is a diagram showing the relationship between the thickness of the dielectric film and the speed of sound in the elastic wave device of the first comparative example and the reference example. 図４は、本発明の第１の実施形態に係る弾性波装置における、誘電体膜の厚みと音速との関係を示す図である。FIG. 4 is a diagram showing the relationship between the thickness of the dielectric film and the speed of sound in the elastic wave device according to the first embodiment of the present invention. 図５は、本発明の第１の実施形態におけるインピーダンス周波数特性を示す図である。FIG. 5 is a diagram showing impedance frequency characteristics according to the first embodiment of the present invention. 図６は、第２の比較例におけるインピーダンス周波数特性を示す図である。FIG. 6 is a diagram showing impedance frequency characteristics in the second comparative example. 図７は、本発明の第１の実施形態の第１の変形例に係る弾性波装置の正面断面図である。FIG. 7 is a front sectional view of an elastic wave device according to a first modification of the first embodiment of the present invention. 図８は、本発明の第１の実施形態の第２の変形例に係る弾性波装置の正面断面図である。FIG. 8 is a front sectional view of an elastic wave device according to a second modification of the first embodiment of the present invention. 図９は、本発明の第１の実施形態の第３の変形例に係る弾性波装置の正面断面図である。FIG. 9 is a front sectional view of an elastic wave device according to a third modification of the first embodiment of the present invention. 図１０は、本発明の第１の実施形態の第４の変形例に係る弾性波装置の正面断面図である。FIG. 10 is a front sectional view of an elastic wave device according to a fourth modification of the first embodiment of the present invention. 図１１は、本発明の第２の実施形態に係る弾性波装置の正面断面図である。FIG. 11 is a front sectional view of the elastic wave device according to the second embodiment of the present invention.
　以下、図面を参照しつつ、本発明の具体的な実施形態を説明することにより、本発明を明らかにする。 Hereinafter, the present invention will be clarified by explaining a specific embodiment of the present invention with reference to the drawings.
　なお、本明細書に記載の各実施形態は、例示的なものであり、異なる実施形態間において、構成の部分的な置換または組み合わせが可能であることを指摘しておく。 It should be noted that each of the embodiments described herein is exemplary and that partial substitutions or combinations of configurations are possible between different embodiments.
　図１は、本発明の第１の実施形態に係る弾性波装置の正面断面図である。図２は、第１の実施形態に係る弾性波装置の平面図である。なお、図１は、図２中のＩ－Ｉ線を通る断面図であり、後述する第１のエッジ領域を通る断面図である。 FIG. 1 is a front sectional view of an elastic wave device according to a first embodiment of the present invention. FIG. 2 is a plan view of the elastic wave device according to the first embodiment. Note that FIG. 1 is a cross-sectional view passing through the line II in FIG. 2, and is a cross-sectional view passing through the first edge region described later.
　図１及び図２に示す弾性波装置１においては、ピストンモードを成立させることにより、横モードを抑制している。弾性波装置１は、圧電性基板２を有する。圧電性基板２上には、ＩＤＴ電極７が設けられている。ＩＤＴ電極７は、複数の電極指を有する。図２に示すように、複数の電極指の先端部と、圧電性基板２との間には、誘電体膜１５Ａ及び誘電体膜１５Ｂが設けられている。 In the elastic wave device 1 shown in FIGS. 1 and 2, the transverse mode is suppressed by establishing the piston mode. The elastic wave device 1 has a piezoelectric substrate 2. An IDT electrode 7 is provided on the piezoelectric substrate 2. The IDT electrode 7 has a plurality of electrode fingers. As shown in FIG. 2, a dielectric film 15A and a dielectric film 15B are provided between the tips of the plurality of electrode fingers and the piezoelectric substrate 2.
　本実施形態の特徴は、誘電体膜１５Ａ及び誘電体膜１５Ｂが、酸化ハフニウム、酸化ニオブ、酸化タングステン及び酸化セリウムからなる群から選択された少なくとも１種の誘電体からなることにある。それによって、ピストンモードをより確実に成立させることができ、横モードをより確実に抑制することができる。上記効果の詳細を、本実施形態の構成の詳細と共に、以下において説明する。 The feature of this embodiment is that the dielectric film 15A and the dielectric film 15B are composed of at least one dielectric selected from the group consisting of hafnium oxide, niobium oxide, tungsten oxide and cerium oxide. Thereby, the piston mode can be established more reliably, and the transverse mode can be suppressed more reliably. The details of the above effects will be described below together with the details of the configuration of the present embodiment.
　図１に示すように、圧電性基板２は、支持基板３と、高音速材料層としての高音速膜４と、低音速膜５と、圧電体層６とを有する。より具体的には、支持基板３上に高音速膜４が設けられている。高音速膜４上に低音速膜５が設けられている。低音速膜５上に圧電体層６が設けられている。 As shown in FIG. 1, the piezoelectric substrate 2 has a support substrate 3, a hypersonic film 4 as a hypersonic material layer, a low sound velocity film 5, and a piezoelectric layer 6. More specifically, the hypersonic film 4 is provided on the support substrate 3. A low sound velocity film 5 is provided on the high sound velocity film 4. The piezoelectric layer 6 is provided on the bass velocity film 5.
　圧電性基板２の圧電体層６上にはＩＤＴ電極７が設けられている。ＩＤＴ電極７に交流電圧を印加することにより、弾性波が励振される。図２に示すように、圧電性基板２上における、ＩＤＴ電極７の弾性波伝搬方向両側に、一対の反射器８及び反射器９が設けられている。弾性波装置１は弾性表面波共振子である。もっとも、本発明に係る弾性波装置は弾性波共振子には限定されず、弾性波共振子を有するフィルタ装置やマルチプレクサであってもよい。 An IDT electrode 7 is provided on the piezoelectric layer 6 of the piezoelectric substrate 2. By applying an AC voltage to the IDT electrode 7, elastic waves are excited. As shown in FIG. 2, a pair of reflectors 8 and reflectors 9 are provided on both sides of the IDT electrode 7 in the elastic wave propagation direction on the piezoelectric substrate 2. The elastic wave device 1 is an elastic surface wave resonator. However, the elastic wave device according to the present invention is not limited to the elastic wave resonator, and may be a filter device or a multiplexer having an elastic wave resonator.
　図２に示すように、ＩＤＴ電極７は、第１のバスバー１６、第２のバスバー１７、複数の第１の電極指１８及び複数の第２の電極指１９を有する。第１のバスバー１６及び第２のバスバー１７は対向している。複数の第１の電極指１８の一端は、それぞれ第１のバスバー１６に接続されている。複数の第２の電極指１９の一端は、それぞれ第２のバスバー１７に接続されている。複数の第１の電極指１８及び複数の第２の電極指１９は互いに間挿し合っている。なお、本明細書においては、弾性波伝搬方向をｘ方向とする。第１の電極指１８及び第２の電極指１９が延びる方向を第１の方向ｙとする。本実施形態においては、ｘ方向とｙ方向とは直交する。 As shown in FIG. 2, the IDT electrode 7 has a first bus bar 16, a second bus bar 17, a plurality of first electrode fingers 18, and a plurality of second electrode fingers 19. The first bus bar 16 and the second bus bar 17 face each other. One end of each of the plurality of first electrode fingers 18 is connected to the first bus bar 16. One end of each of the plurality of second electrode fingers 19 is connected to the second bus bar 17. The plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are interleaved with each other. In this specification, the elastic wave propagation direction is defined as the x direction. The direction in which the first electrode finger 18 and the second electrode finger 19 extend is defined as the first direction y. In this embodiment, the x-direction and the y-direction are orthogonal to each other.
　ＩＤＴ電極７は、主電極層と、２層の密着層とを有する。圧電体層６側から、密着層、主電極層及び密着層がこの順序において積層されている。本明細書において、主電極層は、弾性波の励振において支配的な電極層である。本実施形態においては、２層の密着層は双方共にＴｉ層であり、主電極層はＡｌ層である。もっとも、ＩＤＴ電極７の材料は上記に限定されない。あるいは、ＩＤＴ電極７は主電極層のみからなっていてもよい。反射器８及び反射器９には、ＩＤＴ電極７と同様の材料を用いることができる。 The IDT electrode 7 has a main electrode layer and two adhesion layers. From the piezoelectric layer 6 side, the adhesion layer, the main electrode layer, and the adhesion layer are laminated in this order. In the present specification, the main electrode layer is the dominant electrode layer in the excitation of elastic waves. In the present embodiment, the two close contact layers are both Ti layers, and the main electrode layer is an Al layer. However, the material of the IDT electrode 7 is not limited to the above. Alternatively, the IDT electrode 7 may consist only of the main electrode layer. The same material as the IDT electrode 7 can be used for the reflector 8 and the reflector 9.
　図１に戻り、圧電体層６はタンタル酸リチウム層である。より具体的には、圧電体層６に用いられている圧電体は、５５°ＹカットＸ伝搬ＬｉＴａＯ３である。なお、圧電体層６の材料及びカット角は上記に限定されない。 Returning to FIG. 1, the piezoelectric layer 6 is a lithium tantalate layer. More specifically, the piezoelectric material used in the piezoelectric layer 6 is 55 ° Y-cut X propagation LiTaO 3 . The material and cut angle of the piezoelectric layer 6 are not limited to the above.
　低音速膜５は相対的に低音速な膜である。より具体的には、低音速膜５を伝搬するバルク波の音速は、圧電体層６を伝搬するバルク波の音速よりも低い。本実施形態の低音速膜５は酸化ケイ素膜である。酸化ケイ素はＳｉＯａにより表される。ａは任意の正数である。本実施形態の低音速膜５を構成する酸化ケイ素はＳｉＯ２である。なお、低音速膜５の材料は上記に限定されず、例えば、ガラス、酸窒化ケイ素、酸化リチウム、五酸化タンタル、または、酸化ケイ素にフッ素、炭素やホウ素を加えた化合物を主成分とする材料を用いることもできる。 The low sound velocity film 5 is a relatively low sound velocity film. More specifically, the sound velocity of the bulk wave propagating in the bass velocity film 5 is lower than the sound velocity of the bulk wave propagating in the piezoelectric layer 6. The bass velocity film 5 of the present embodiment is a silicon oxide film. Silicon oxide is represented by SiO a. a is an arbitrary positive number. The silicon oxide constituting the bass velocity film 5 of the present embodiment is SiO 2 . The material of the bass velocity film 5 is not limited to the above, and is, for example, a material containing glass, silicon nitride, lithium oxide, tantalum pentoxide, or a compound obtained by adding fluorine, carbon, or boron to silicon oxide as a main component. Can also be used.
　本実施形態では、高音速材料層は高音速膜４である。高音速材料層は相対的に高音速な層である。より具体的には、高音速材料層を伝搬するバルク波の音速は、圧電体層６を伝搬する弾性波の音速よりも高い。本実施形態においては、高音速材料層としての高音速膜４は窒化ケイ素膜である。なお、本実施形態の高音速膜４を構成する窒化ケイ素はＳｉＮである。もっとも、高音速膜４の材料は上記に限定されず、例えば、シリコン、酸化アルミニウム、炭化ケイ素、酸窒化ケイ素、サファイア、タンタル酸リチウム、ニオブ酸リチウム、水晶、アルミナ、ジルコニア、コージライト、ムライト、ステアタイト、フォルステライト、マグネシア、ＤＬＣ（ダイヤモンドライクカーボン）膜またはダイヤモンドなど、上記材料を主成分とする媒質を用いることもできる。 In this embodiment, the hypersonic material layer is the hypersonic film 4. The hypersonic material layer is a relatively hypersonic layer. More specifically, the sound velocity of the bulk wave propagating in the hypersonic material layer is higher than the sound velocity of the elastic wave propagating in the piezoelectric layer 6. In the present embodiment, the hypersonic film 4 as the hypersonic material layer is a silicon nitride film. The silicon nitride constituting the hypersonic film 4 of the present embodiment is SiN. However, the material of the treble velocity film 4 is not limited to the above, and for example, silicon, aluminum oxide, silicon carbide, silicon nitride, sapphire, lithium tantalate, lithium niobate, crystal, alumina, zirconia, cordierite, mulite, etc. A medium containing the above materials as a main component, such as steatite, forsterite, magnesia, DLC (diamond-like carbon) film, or diamond, can also be used.
　本実施形態では、支持基板３はシリコン基板である。なお、支持基板３の材料は上記に限定されず、例えば、酸化アルミニウム、タンタル酸リチウム、ニオブ酸リチウム、水晶などの圧電体、アルミナ、サファイア、マグネシア、窒化ケイ素、窒化アルミニウム、炭化ケイ素、ジルコニア、コージライト、ムライト、ステアタイト、フォルステライトなどの各種セラミック、ダイヤモンド、ガラスなどの誘電体、窒化ガリウムなどの半導体または樹脂などを用いることもできる。 In this embodiment, the support substrate 3 is a silicon substrate. The material of the support substrate 3 is not limited to the above, and for example, piezoelectric materials such as aluminum oxide, lithium tantalate, lithium niobate, and crystal, alumina, sapphire, magnesia, silicon nitride, aluminum nitride, silicon carbide, zirconia, and the like. Various ceramics such as cozilite, mulite, steatite, and forsterite, dielectrics such as diamond and glass, semiconductors or resins such as gallium nitride can also be used.
　本実施形態においては、圧電性基板２が、高音速材料層としての高音速膜４、低音速膜５及び圧電体層６がこの順序において積層された構造を有する。それによって、弾性波のエネルギーを圧電体層６側に効果的に閉じ込めることができる。 In the present embodiment, the piezoelectric substrate 2 has a structure in which the hypersonic film 4, the hypersonic film 5 and the piezoelectric layer 6 as the hypersonic material layer are laminated in this order. Thereby, the energy of the elastic wave can be effectively confined on the piezoelectric layer 6 side.
　図２に示すように、ＩＤＴ電極７において、第１の電極指１８と第２の電極指１９とがｘ方向において重なり合っている部分は、交叉領域Ａである。交叉領域Ａは、中央領域Ｃ、第１のエッジ領域Ｅ１及び第２のエッジ領域Ｅ２を有する。中央領域Ｃは、交叉領域Ａにおいて、ｙ方向における中央側に位置している。第１のエッジ領域Ｅ１及び第２のエッジ領域Ｅ２は、中央領域Ｃのｙ方向両側に配置されている。より具体的には、第１のエッジ領域Ｅ１は、中央領域Ｃの第１のバスバー１６側に配置されている。第２のエッジ領域Ｅ２は、中央領域Ｃの第２のバスバー１７側に配置されている。なお、以下において、第１のエッジ領域Ｅ１及び第２のエッジ領域Ｅ２を単にエッジ領域と記載することもある。 As shown in FIG. 2, in the IDT electrode 7, the portion where the first electrode finger 18 and the second electrode finger 19 overlap in the x direction is the crossing region A. The crossing region A has a central region C, a first edge region E1 and a second edge region E2. The central region C is located on the central side in the y direction in the crossing region A. The first edge region E1 and the second edge region E2 are arranged on both sides of the central region C in the y direction. More specifically, the first edge region E1 is arranged on the first bus bar 16 side of the central region C. The second edge region E2 is arranged on the second bus bar 17 side of the central region C. In the following, the first edge region E1 and the second edge region E2 may be simply referred to as an edge region.
　ＩＤＴ電極７は、第１のギャップ領域Ｇ１及び第２のギャップ領域Ｇ２を有する。第１のギャップ領域Ｇ１は、第１のエッジ領域Ｅ１及び第１のバスバー１６の間に位置する。第２のギャップ領域Ｇ２は、第２のエッジ領域Ｅ２及び第２のバスバー１７の間に位置する。第１のギャップ領域Ｇ１においては、第１の電極指１８及び第２の電極指１９のうち第１の電極指１８のみが設けられている。これにより、第１のギャップ領域Ｇ１における音速は中央領域Ｃにおける音速よりも高い。同様に、第２のギャップ領域Ｇ２においては、第１の電極指１８及び第２の電極指１９のうち第２の電極指１９のみが設けられている。これにより、第２のギャップ領域Ｇ２における音速は中央領域Ｃにおける音速よりも高い。中央領域Ｃにおける音速をＶｃとし、第１のギャップ領域Ｇ１及び第２のギャップ領域Ｇ２における音速をＶｇとしたときに、Ｖｃ＜Ｖｇである。このように、第１のギャップ領域Ｇ１及び第２のギャップ領域Ｇ２において、高音速領域が構成されている。 The IDT electrode 7 has a first gap region G1 and a second gap region G2. The first gap region G1 is located between the first edge region E1 and the first bus bar 16. The second gap region G2 is located between the second edge region E2 and the second bus bar 17. In the first gap region G1, only the first electrode finger 18 of the first electrode finger 18 and the second electrode finger 19 is provided. As a result, the speed of sound in the first gap region G1 is higher than the speed of sound in the central region C. Similarly, in the second gap region G2, only the second electrode finger 19 of the first electrode finger 18 and the second electrode finger 19 is provided. As a result, the speed of sound in the second gap region G2 is higher than the speed of sound in the central region C. When the speed of sound in the central region C is Vc and the speed of sound in the first gap region G1 and the second gap region G2 is Vg, Vc <Vg. As described above, the high sound velocity region is configured in the first gap region G1 and the second gap region G2.
　ここで、第１のエッジ領域Ｅ１において、圧電性基板２と全ての第１の電極指１８及び全ての第２の電極指１９との間に、１個の上記誘電体膜１５Ａが設けられている。誘電体膜１５Ａは帯状の形状を有する。誘電体膜１５Ａは、圧電性基板２上における、全ての電極指間の部分にも設けられている。さらに、誘電体膜１５Ａは、圧電性基板２と、反射器８及び反射器９との間にも設けられている。同様に、第２のエッジ領域Ｅ２において、圧電性基板２と全ての第１の電極指１８及び全ての第２の電極指１９との間に、１個の上記誘電体膜１５Ｂが設けられている。誘電体膜１５Ｂは帯状の形状を有する。誘電体膜１５Ｂは、圧電性基板２上における、全ての電極指間の部分にも設けられている。さらに、誘電体膜１５Ｂは、圧電性基板２と、反射器８及び反射器９との間にも設けられている。もっとも、誘電体膜１５Ａ及び誘電体膜１５Ｂは、圧電性基板２と反射器８及び反射器９との間には設けられていなくともよい。 Here, in the first edge region E1, one dielectric film 15A is provided between the piezoelectric substrate 2, all the first electrode fingers 18, and all the second electrode fingers 19. There is. The dielectric film 15A has a band-like shape. The dielectric film 15A is also provided on the piezoelectric substrate 2 between all the electrode fingers. Further, the dielectric film 15A is also provided between the piezoelectric substrate 2 and the reflector 8 and the reflector 9. Similarly, in the second edge region E2, one dielectric film 15B is provided between the piezoelectric substrate 2 and all the first electrode fingers 18 and all the second electrode fingers 19. There is. The dielectric film 15B has a band-like shape. The dielectric film 15B is also provided on the piezoelectric substrate 2 between all the electrode fingers. Further, the dielectric film 15B is also provided between the piezoelectric substrate 2 and the reflector 8 and the reflector 9. However, the dielectric film 15A and the dielectric film 15B do not have to be provided between the piezoelectric substrate 2 and the reflector 8 and the reflector 9.
　なお、１個の誘電体膜１５Ａが、圧電性基板２と、ＩＤＴ電極７の全ての電極指との間に設けられている構成には限定されない。弾性波装置１は、複数の誘電体膜１５Ａを有していてもよい。誘電体膜１５Ａは、圧電性基板２と、ＩＤＴ電極７の少なくとも１本の電極指との間に設けられていればよい。誘電体膜１５Ａは、圧電性基板２上における、複数の電極指間の部分には設けられていなくともよい。もっとも、複数の誘電体膜１５Ａが設けられている場合、圧電性基板２と全ての電極指との間に、誘電体膜１５Ａがそれぞれ設けられていることが好ましい。 Note that the configuration is not limited to the configuration in which one dielectric film 15A is provided between the piezoelectric substrate 2 and all the electrode fingers of the IDT electrode 7. The elastic wave device 1 may have a plurality of dielectric films 15A. The dielectric film 15A may be provided between the piezoelectric substrate 2 and at least one electrode finger of the IDT electrode 7. The dielectric film 15A does not have to be provided in the portion between the plurality of electrode fingers on the piezoelectric substrate 2. However, when a plurality of dielectric films 15A are provided, it is preferable that the dielectric films 15A are provided between the piezoelectric substrate 2 and all the electrode fingers.
　同様に、弾性波装置１は、複数の誘電体膜１５Ｂを有していてもよい。誘電体膜１５Ｂは、圧電性基板２と、ＩＤＴ電極７の少なくとも１本の電極指との間に設けられていればよい。誘電体膜１５Ｂは、圧電性基板２上における、複数の電極指間の部分には設けられていなくともよい。もっとも、複数の誘電体膜１５Ｂが設けられている場合、圧電性基板２と全ての電極指との間に、誘電体膜１５Ｂがそれぞれ設けられていることが好ましい。 Similarly, the elastic wave device 1 may have a plurality of dielectric films 15B. The dielectric film 15B may be provided between the piezoelectric substrate 2 and at least one electrode finger of the IDT electrode 7. The dielectric film 15B does not have to be provided in the portion between the plurality of electrode fingers on the piezoelectric substrate 2. However, when a plurality of dielectric films 15B are provided, it is preferable that the dielectric films 15B are provided between the piezoelectric substrate 2 and all the electrode fingers.
　本実施形態においては、誘電体膜１５Ａ及び誘電体膜１５Ｂが、酸化ハフニウム、酸化ニオブ、酸化タングステン及び酸化セリウムからなる群から選択された少なくとも１種の誘電体からなる。それによって、第１のエッジ領域Ｅ１及び第２のエッジ領域Ｅ２において、音速をより確実に低くすることができる。第１のエッジ領域Ｅ１及び第２のエッジ領域Ｅ２における音速をＶｅとしたときに、Ｖｅ＜Ｖｃとすることができる。このように、第１のエッジ領域Ｅ１及び第２のエッジ領域Ｅ２において、低音速領域がより確実に構成される。Ｖｅ＜Ｖｃ、すなわちＶｅ／Ｖｃ＜１とすることができる効果の詳細を以下において示す。 In the present embodiment, the dielectric film 15A and the dielectric film 15B are made of at least one dielectric selected from the group consisting of hafnium oxide, niobium oxide, tungsten oxide and cerium oxide. Thereby, the speed of sound can be more reliably lowered in the first edge region E1 and the second edge region E2. When the speed of sound in the first edge region E1 and the second edge region E2 is Ve, Ve <Vc can be set. In this way, the bass sound region is more reliably configured in the first edge region E1 and the second edge region E2. The details of the effect that can be Ve <Vc, that is, Ve / Vc <1 are shown below.
　第１の実施形態の構成を有する弾性波装置、第１の比較例及び参考例において、音速の変化の挙動を比較した。より具体的には、誘電体膜の膜厚の変化に対する、音速の変化の挙動を比較した。音速は、共振周波数を測定することによって算出した。より詳細には、音速をＶ、周波数をｆ、ＩＤＴ電極の電極指ピッチにより規定される波長をλとしたとき、Ｖ＝ｆλの関係が成立する。この関係から音速を算出した。 The behavior of changes in sound velocity was compared in the elastic wave device having the configuration of the first embodiment, the first comparative example, and the reference example. More specifically, the behavior of the change in sound velocity with respect to the change in the film thickness of the dielectric film was compared. The speed of sound was calculated by measuring the resonance frequency. More specifically, when the speed of sound is V, the frequency is f, and the wavelength defined by the electrode finger pitch of the IDT electrode is λ, the relationship of V = fλ is established. The speed of sound was calculated from this relationship.
　第１の実施形態においては、誘電体膜がＨｆＯ２膜、Ｎｂ２Ｏ５膜、ＷＯ３膜及びＣｅＯ２膜である場合のそれぞれにおいて、音速の挙動を調べた。第１の比較例においては、誘電体膜に用いた誘電体が第１の実施形態と異なる。第１の比較例として、誘電体膜がＳｉＯ２膜及びＳｉＮ膜である場合のそれぞれにおいて、音速の挙動を調べた。参考例は、誘電体膜がＩＤＴ電極上に設けられており、かつ誘電体膜がＳｉＯ２膜である点において、第１の実施形態と異なる。なお、誘電体膜が設けられていない場合においても、音速を測定した。 In the first embodiment, the behavior of the speed of sound was investigated in each of the cases where the dielectric film was an HfO 2 film, an Nb 2 O 5 film, a WO 3 film, and a CeO 2 film. In the first comparative example, the dielectric used for the dielectric film is different from that of the first embodiment. As a first comparative example, the behavior of the speed of sound was investigated in each of the cases where the dielectric film was a SiO 2 film and a SiN film. The reference example differs from the first embodiment in that the dielectric film is provided on the IDT electrode and the dielectric film is the SiO 2 film. The speed of sound was measured even when the dielectric film was not provided.
　第１の実施形態の構成を有する弾性波装置、並びに第１の比較例及び参考例の弾性波装置の設計パラメータは以下の通りである。 The design parameters of the elastic wave device having the configuration of the first embodiment and the elastic wave device of the first comparative example and the reference example are as follows.
　支持基板；材料…Ｓｉ
　高音速膜；材料…ＳｉＮ、厚み…３００ｎｍ
　低音速膜；材料…ＳｉＯ２、厚み…３００ｎｍ
　圧電体層；材料…５５°ＹカットＸ伝搬ＬｉＴａＯ３、厚み…４００ｎｍ
　ＩＤＴ電極の層構成；層構成…圧電体層側からＴｉ層／Ａｌ層／Ｔｉ層、厚み…圧電体層側から１２ｎｍ／１００ｎｍ／４ｎｍ
　ＩＤＴ電極の波長；２μｍ
　ＩＤＴ電極のデューティ比；０．５
　誘電体膜；厚み…５ｎｍ以上、６５ｎｍ以下の範囲、または５ｎｍ以上、５５ｎｍ以下の範囲において、１０ｎｍ刻みで変化させた。 Support substrate; Material ... Si
Hypersonic film; Material: SiN, Thickness: 300 nm
Bass velocity film; Material: SiO 2 , Thickness: 300 nm
Piezoelectric layer; Material: 55 ° Y-cut X propagation LiTaO 3 , Thickness: 400 nm
Layer structure of IDT electrode; Layer structure: Ti layer / Al layer / Ti layer from the piezoelectric layer side, thickness: 12 nm / 100 nm / 4 nm from the piezoelectric layer side
IDT electrode wavelength; 2 μm
IDT electrode duty ratio; 0.5
Dielectric film; Thickness: 5 nm or more, 65 nm or less, or 5 nm or more, 55 nm or less, changed in 10 nm increments.
　図３は、第１の比較例及び参考例の弾性波装置における、誘電体膜の厚みと音速との関係を示す図である。図４は、第１の実施形態に係る弾性波装置における、誘電体膜の厚みと音速との関係を示す図である。 FIG. 3 is a diagram showing the relationship between the thickness of the dielectric film and the speed of sound in the elastic wave device of the first comparative example and the reference example. FIG. 4 is a diagram showing the relationship between the thickness of the dielectric film and the speed of sound in the elastic wave device according to the first embodiment.
　図３に示すように、第１の比較例においては、誘電体膜がＳｉＯ２膜である場合には、誘電体膜が設けられていない場合よりも音速が高くなっている。さらに、誘電体膜が厚くなるほど、音速が高くなっている。誘電体膜がＳｉＮ膜である場合においても同様に、誘電体膜が厚くなるほど、音速が高くなっている。なお、参考例のように、誘電体膜がＳｉＯ２膜であっても、誘電体膜がＩＤＴ電極上に設けられている場合には、誘電体膜が厚くなるほど、音速が低くなっている。 As shown in FIG. 3, in the first comparative example, when the dielectric film is a SiO 2 film, the speed of sound is higher than when the dielectric film is not provided. Further, the thicker the dielectric film, the higher the speed of sound. Similarly, when the dielectric film is a SiN film, the thicker the dielectric film, the higher the speed of sound. Even if the dielectric film is a SiO 2 film as in the reference example, when the dielectric film is provided on the IDT electrode, the thicker the dielectric film, the lower the speed of sound.
　一方、図４に示すように、第１の実施形態においては、誘電体膜１５Ａ及び誘電体膜１５ＢがＨｆＯ２膜、Ｎｂ２Ｏ５膜、ＷＯ３膜及びＣｅＯ２膜である場合のそれぞれにおいて、誘電体膜１５Ａ及び誘電体膜１５Ｂが厚くなるほど、音速が低くなっていることがわかる。このように、第１の実施形態においては、第１のエッジ領域Ｅ１及び第２のエッジ領域Ｅ２において、低音速領域をより確実に構成することができる。 On the other hand, as shown in FIG. 4, in the first embodiment, in each of the cases where the dielectric film 15A and the dielectric film 15B are the HfO 2 film, the Nb 2 O 5 film, the WO 3 film, and the CeO 2 film. It can be seen that the thicker the dielectric film 15A and the dielectric film 15B, the lower the sound velocity. As described above, in the first embodiment, the low sound velocity region can be more reliably configured in the first edge region E1 and the second edge region E2.
　従って、第１の実施形態においては、ｙ方向において、中央領域Ｃの外側に低音速領域をより確実に配置することができる。さらに、低音速領域の外側に高音速領域が位置する。よって、ピストンモードをより確実に成立させることができる。従って、横モードをより確実に抑制することができる。 Therefore, in the first embodiment, the low sound velocity region can be more reliably arranged outside the central region C in the y direction. Further, the high sound velocity region is located outside the low sound velocity region. Therefore, the piston mode can be established more reliably. Therefore, the transverse mode can be suppressed more reliably.
　さらに、本発明者は、横モードの抑制が、誘電体膜１５Ａ及び誘電体膜１５Ｂの誘電率に依存することを見出した。この詳細を以下において説明する。 Furthermore, the present inventor has found that the suppression of the transverse mode depends on the dielectric constants of the dielectric film 15A and the dielectric film 15B. The details will be described below.
　第１の実施形態及び第２の比較例において、シミュレーションにより、インピーダンス周波数特性を比較した。第１の実施形態においては、誘電体膜として、ＨｆＯ２膜を用いた。第２の比較例においては、誘電体膜の弾性定数及び密度をＨｆＯ２膜の弾性定数及び密度とし、誘電体膜の誘電率をＳｉＯ２膜の誘電率とした。なお、第１の実施形態の構成を有する弾性波装置及び第２の比較例の弾性波装置の設計パラメータは、誘電体膜の厚み以外は、上記音速の挙動の比較の場合と同様である。誘電体膜の厚みは３０ｎｍとした。 In the first embodiment and the second comparative example, the impedance frequency characteristics were compared by simulation. In the first embodiment, an HfO 2 film was used as the dielectric film. In the second comparative example, the elastic constant and density of the dielectric film were defined as the elastic constant and density of the HfO 2 film, and the dielectric constant of the dielectric film was defined as the dielectric constant of the SiO 2 film. The design parameters of the elastic wave device having the configuration of the first embodiment and the elastic wave device of the second comparative example are the same as in the case of comparing the behavior of the sound velocity except for the thickness of the dielectric film. The thickness of the dielectric film was 30 nm.
　図５は、第１の実施形態におけるインピーダンス周波数特性を示す図である。図６は、第２の比較例におけるインピーダンス周波数特性を示す図である。 FIG. 5 is a diagram showing impedance frequency characteristics in the first embodiment. FIG. 6 is a diagram showing impedance frequency characteristics in the second comparative example.
　図５に示すように、第１の実施形態においては、横モードは抑制されている。他方、図６中の矢印Ｂに示すように、第２の比較例においては、横モードによる大きなスプリアスが生じている。誘電体膜の弾性定数及び密度がＨｆＯ２膜の弾性定数及び密度と同じであっても、誘電体膜の誘電率がＳｉＯ２膜の誘電率と同じであれば、横モードを抑制し難いことがわかる。このように、横モードの抑制が、誘電体膜の誘電率に依存することがわかる。 As shown in FIG. 5, in the first embodiment, the transverse mode is suppressed. On the other hand, as shown by the arrow B in FIG. 6, in the second comparative example, a large spurious due to the transverse mode is generated. Even if the elastic constant and density of the dielectric film are the same as the elastic constant and density of the HfO 2 film, if the dielectric constant of the dielectric film is the same as the dielectric constant of the SiO 2 film, it is difficult to suppress the transverse mode. I understand. As described above, it can be seen that the suppression of the transverse mode depends on the dielectric constant of the dielectric film.
　ここで、弾性波装置における誘電体膜の誘電率などを変化させて、音速Ｖｃ及び音速Ｖｅの関係を調べた。これにより、エッジ領域における音速を低くすることができる条件を導出した。この詳細を以下において説明する。 Here, the relationship between the sound velocity Vc and the sound velocity Ve was investigated by changing the permittivity of the dielectric film in the elastic wave device. As a result, the conditions under which the speed of sound in the edge region can be lowered were derived. The details will be described below.
　上記のように、ＩＤＴ電極の電極指ピッチにより規定される波長をλとする。電極指ピッチとは、隣り合う電極指における電極指中心間距離をいう。具体的には、隣り合う電極指のそれぞれにおいて、ｘ方向における中心点同士を結んだ距離をいう。電極指中心間距離が一定でない場合には、電極指ピッチは、電極指中心間距離の平均値であるとする。さらに、誘電体膜の厚みをｔ＿Ｄ［λ］、誘電体膜の誘電率をε、誘電体膜の密度をｄ［ｋｇ／ｍ３］、誘電体膜のヤング率をＹ［ＧＰａ］、圧電体層の厚みをｔ＿ＬＴ［λ］、ＩＤＴ電極の主電極層の厚みをｔ＿Ａｌ［λ］とし、中央領域における音速をＶｃ、一対のエッジ領域における音速をＶｅとする。上記各パラメータを変化させて、それぞれの条件において、Ｖｅ／Ｖｃを算出した。弾性波装置の設計パラメータは以下の通りである。なお、以下においては、上記各パラメータの単位を省略して記載することもある。 As described above, let λ be the wavelength defined by the electrode finger pitch of the IDT electrode. The electrode finger pitch refers to the distance between the center of the electrode fingers in the adjacent electrode fingers. Specifically, it refers to the distance connecting the center points in the x direction of each of the adjacent electrode fingers. When the distance between the center of the electrode fingers is not constant, the electrode finger pitch is assumed to be the average value of the distances between the center of the electrode fingers. Further, the thickness of the dielectric film is t_D [λ], the dielectric constant of the dielectric film is ε, the density of the dielectric film is d [kg / m 3 ], the Young ratio of the dielectric film is Y [GPa], and the piezoelectric material. The thickness of the layer is t_LT [λ], the thickness of the main electrode layer of the IDT electrode is t_Al [λ], the speed of sound in the central region is Vc, and the speed of sound in the pair of edge regions is Ve. Ve / Vc was calculated under each condition by changing each of the above parameters. The design parameters of the elastic wave device are as follows. In the following, the unit of each of the above parameters may be omitted.
　支持基板；材料…Ｓｉ
　高音速膜；材料…ＳｉＮ、厚み…３００ｎｍ
　低音速膜；材料…ＳｉＯ２、厚み…３００ｎｍ
　圧電体層；材料…５５°ＹカットＸ伝搬ＬｉＴａＯ３、厚み…ｔ＿ＬＴ
　ＩＤＴ電極の層構成；層構成…圧電体層側からＴｉ層／Ａｌ層／Ｔｉ層、厚み…圧電体層側から１２ｎｍ／ｔ＿Ａｌ／４ｎｍ
　ＩＤＴ電極の波長；２μｍ
　ＩＤＴ電極のデューティ比；０．５
　誘電体膜の密度ｄ；２ｋｇ／ｍ３以上、８ｋｇ／ｍ３以下の範囲において、２ｋｇ／ｍ３刻みで変化させた。
　誘電体膜のヤング率Ｙ；７０ＧＰａ以上、２８０ＧＰａ以下の範囲において、７０ＧＰａ刻みで変化させた。
　誘電体膜の誘電率ε；５以上、３５以下の範囲において、５刻みで変化させた。
　誘電体膜の厚みｔ＿Ｄ；０．００２５λ以上、０．０１７５λ以下の範囲において、０．００２５λ刻みで変化させた。
　圧電体層の厚みｔ＿ＬＴ；０．１５λ以上、０．３λ以下の範囲において、０．０５λ刻みで変化させた。
　Ａｌ層の厚みｔ＿Ａｌ；０．０５λ以上、０．０７５λ以下の範囲において、０．０１２５λ刻みで変化させた。 Support substrate; Material ... Si
Hypersonic film; Material: SiN, Thickness: 300 nm
Bass velocity film; Material: SiO 2 , Thickness: 300 nm
Piezoelectric layer; Material: 55 ° Y-cut X propagation LiTaO 3 , Thickness: t_LT
Layer structure of IDT electrode; Layer structure: Ti layer / Al layer / Ti layer from the piezoelectric layer side, thickness: 12 nm / t_Al / 4 nm from the piezoelectric layer side
IDT electrode wavelength; 2 μm
IDT electrode duty ratio; 0.5
The density of the dielectric film d; 2kg / m 3 or more, in 8 kg / m 3 or less of the range was varied 2 kg / m 3 increments.
The Young's modulus of the dielectric film was changed in 70 GPa increments in the range of 70 GPa or more and 280 GPa or less.
The dielectric constant of the dielectric film was changed in increments of 5 in the range of ε; 5 or more and 35 or less.
The thickness of the dielectric film t_D; was changed in 0.0025λ increments in the range of 0.0025λ or more and 0.0175λ or less.
The thickness of the piezoelectric layer t_LT; was changed in 0.05λ increments in the range of 0.15λ or more and 0.3λ or less.
The thickness of the Al layer t_Al; was changed in 0.0125λ increments in the range of 0.05λ or more and 0.075λ or less.
　これらにより、上記各パラメータとＶｅ／Ｖｃとの関係式である式１を導出した。 From these, the equation 1 which is the relational expression between each of the above parameters and Ve / Vc was derived.
Figure JPOXMLDOC01-appb-M000003
Figure JPOXMLDOC01-appb-M000003
　ｔ＿Ｄ［λ］、ε、ｄ［ｋｇ／ｍ３］、Ｙ［ＧＰａ］、ｔ＿ＬＴ［λ］及びｔ＿Ａｌ［λ］が、式１により導出されるＶｅ／Ｖｃが１未満となる値であればよい。それによって、一対のエッジ領域を確実に低音速領域とすることができる。これにより、ピストンモードを成立させることができ、横モードを抑制することができる。 t_D [λ], ε, d [kg / m 3 ], Y [GPa], t_LT [λ] and t_Al [λ] may be values such that Ve / Vc derived by Equation 1 is less than 1. .. Thereby, the pair of edge regions can be surely set as the low sound velocity region. As a result, the piston mode can be established and the transverse mode can be suppressed.
　なお、上記各パラメータが、式１により導出されるＶｅ／Ｖｃが１未満となる値である場合には、図２に示す誘電体膜１５Ａ及び誘電体膜１５Ｂは、酸化ハフニウム、酸化ニオブ、酸化タングステン及び酸化セリウムを含まなくともよい。もっとも、誘電体膜１５Ａ及び誘電体膜１５Ｂが、酸化ハフニウム、酸化ニオブ、酸化タングステン及び酸化セリウムからなる群から選択された少なくとも１種の誘電体からなることが好ましい。 When each of the above parameters has a value in which Ve / Vc derived by Equation 1 is less than 1, the dielectric film 15A and the dielectric film 15B shown in FIG. 2 are composed of hafnium oxide, niobium oxide, and oxidation. It does not have to contain tungsten and cerium oxide. However, it is preferable that the dielectric film 15A and the dielectric film 15B are made of at least one dielectric selected from the group consisting of hafnium oxide, niobium oxide, tungsten oxide and cerium oxide.
　上述したように、第１の実施形態の圧電性基板２においては、高音速膜４上に、低音速膜５を介して間接的に圧電体層６が設けられている。もっとも、圧電性基板２の構成は上記に限定されない。以下において、圧電性基板の構成のみが第１の実施形態と異なる、第１の実施形態の第１～第３の変形例を示す。第１～第３の変形例においても、第１の実施形態と同様に、横モードをより確実に抑制することができる。加えて、弾性波のエネルギーを圧電体層６側に効果的に閉じ込めることができる。 As described above, in the piezoelectric substrate 2 of the first embodiment, the piezoelectric layer 6 is indirectly provided on the hypersonic film 4 via the hypersonic film 5. However, the configuration of the piezoelectric substrate 2 is not limited to the above. In the following, first to third modifications of the first embodiment, in which only the configuration of the piezoelectric substrate is different from that of the first embodiment, will be shown. Also in the first to third modifications, the transverse mode can be suppressed more reliably as in the first embodiment. In addition, the energy of elastic waves can be effectively confined to the piezoelectric layer 6 side.
　図７に示す第１の変形例においては、圧電性基板２２Ａは、支持基板３と、高音速膜４と、圧電体層６とを有する。本変形例においては、高音速材料層としての高音速膜４上に、直接的に圧電体層６が設けられている。 In the first modification shown in FIG. 7, the piezoelectric substrate 22A has a support substrate 3, a hypersonic film 4, and a piezoelectric layer 6. In this modification, the piezoelectric layer 6 is directly provided on the hypersonic film 4 as the hypersonic material layer.
　図８に示す第２の変形例においては、高音速材料層は高音速支持基板２４である。圧電性基板２２Ｂは、高音速支持基板２４と、低音速膜５と、圧電体層６とを有する。高音速支持基板２４上に低音速膜５が設けられている。 In the second modification shown in FIG. 8, the hypersonic material layer is the hypersonic support substrate 24. The piezoelectric substrate 22B has a hypersonic support substrate 24, a low sound velocity film 5, and a piezoelectric layer 6. The hypersonic film 5 is provided on the hypersonic support substrate 24.
　高音速支持基板２４の材料としては、例えば、酸化アルミニウム、炭化ケイ素、窒化ケイ素、酸窒化ケイ素、シリコン、サファイア、タンタル酸リチウム、ニオブ酸リチウム、水晶、アルミナ、ジルコニア、コージライト、ムライト、ステアタイト、フォルステライト、マグネシア、ＤＬＣ膜またはダイヤモンドなど、上記材料を主成分とする媒質を用いることができる。 Examples of the material of the high-pitched sound support substrate 24 include aluminum oxide, silicon carbide, silicon nitride, silicon nitride, silicon, sapphire, lithium tantrate, lithium niobate, crystal, alumina, zirconia, cordierite, mulite, and steatite. , Forsterite, magnesia, DLC film, diamond, or the like, or a medium containing the above-mentioned material as a main component can be used.
　図９に示す第３の変形例においては、圧電性基板２２Ｃは、高音速支持基板２４と、圧電体層６とを有する。本変形例においては、高音速材料層としての高音速支持基板２４上に、直接的に圧電体層６が設けられている。 In the third modification shown in FIG. 9, the piezoelectric substrate 22C has a hypersonic support substrate 24 and a piezoelectric layer 6. In this modification, the piezoelectric layer 6 is directly provided on the hypersonic support substrate 24 as the hypersonic material layer.
　一方で、図１０に示す第１の実施形態の第４の変形例においては、圧電性基板２２Ｄは、圧電体層のみからなる。圧電性基板２２Ｄは圧電基板である。この場合においても、第１の実施形態と同様に、横モードをより確実に抑制することができる。 On the other hand, in the fourth modification of the first embodiment shown in FIG. 10, the piezoelectric substrate 22D is composed of only the piezoelectric layer. The piezoelectric substrate 22D is a piezoelectric substrate. In this case as well, the transverse mode can be suppressed more reliably, as in the first embodiment.
　図１１は、第２の実施形態に係る弾性波装置の正面断面図である。 FIG. 11 is a front sectional view of the elastic wave device according to the second embodiment.
　本実施形態は、圧電性基板３２が、音響反射膜３７を有する点において、第１の実施形態と異なる。より具体的には、圧電性基板３２は、支持基板３と、音響反射膜３７と、圧電体層６とを有する。支持基板３上に音響反射膜３７が設けられている。音響反射膜３７上に圧電体層６が設けられている。上記の点以外においては、本実施形態の弾性波装置３１は第１の実施形態の弾性波装置１と同様の構成を有する。 This embodiment is different from the first embodiment in that the piezoelectric substrate 32 has an acoustic reflection film 37. More specifically, the piezoelectric substrate 32 has a support substrate 3, an acoustic reflection film 37, and a piezoelectric layer 6. An acoustic reflection film 37 is provided on the support substrate 3. The piezoelectric layer 6 is provided on the acoustic reflection film 37. Except for the above points, the elastic wave device 31 of the present embodiment has the same configuration as the elastic wave device 1 of the first embodiment.
　音響反射膜３７は複数の音響インピーダンス層の積層体である。より具体的には、音響反射膜３７は、複数の低音響インピーダンス層と、複数の高音響インピーダンス層とを有する。低音響インピーダンス層は、相対的に音響インピーダンスが低い層である。音響反射膜３７の複数の低音響インピーダンス層は、低音響インピーダンス層３５ａ及び低音響インピーダンス層３５ｂである。一方で、高音響インピーダンス層は、相対的に音響インピーダンスが高い層である。音響反射膜３７の複数の高音響インピーダンス層は、高音響インピーダンス層３４ａ及び高音響インピーダンス層３４ｂである。低音響インピーダンス層及び高音響インピーダンス層は交互に積層されている。なお、低音響インピーダンス層３５ａが、音響反射膜３７において最も圧電体層６側に位置する層である。 The acoustic reflection film 37 is a laminate of a plurality of acoustic impedance layers. More specifically, the acoustic reflection film 37 has a plurality of low acoustic impedance layers and a plurality of high acoustic impedance layers. The low acoustic impedance layer is a layer having a relatively low acoustic impedance. The plurality of low acoustic impedance layers of the acoustic reflection film 37 are a low acoustic impedance layer 35a and a low acoustic impedance layer 35b. On the other hand, the high acoustic impedance layer is a layer having a relatively high acoustic impedance. The plurality of high acoustic impedance layers of the acoustic reflection film 37 are a high acoustic impedance layer 34a and a high acoustic impedance layer 34b. The low acoustic impedance layer and the high acoustic impedance layer are alternately laminated. The low acoustic impedance layer 35a is a layer located closest to the piezoelectric layer 6 in the acoustic reflection film 37.
　音響反射膜３７は、低音響インピーダンス層及び高音響インピーダンス層をそれぞれ２層ずつ有する。もっとも、音響反射膜３７は、低音響インピーダンス層及び高音響インピーダンス層をそれぞれ少なくとも１層ずつ有していればよい。 The acoustic reflection film 37 has two layers each of a low acoustic impedance layer and a high acoustic impedance layer. However, the acoustic reflection film 37 may have at least one low acoustic impedance layer and one high acoustic impedance layer.
　低音響インピーダンス層の材料としては、例えば、酸化ケイ素またはアルミニウムなどを用いることができる。高音響インピーダンス層の材料としては、例えば、白金またはタングステンなどの金属や、窒化アルミニウムまたは窒化ケイ素などの誘電体を用いることができる。 As the material of the low acoustic impedance layer, for example, silicon oxide or aluminum can be used. As the material of the high acoustic impedance layer, for example, a metal such as platinum or tungsten or a dielectric material such as aluminum nitride or silicon nitride can be used.
　弾性波装置３１は、音響反射膜３７を有するため、弾性波のエネルギーを圧電体層６側に効果的に閉じ込めることができる。 Since the elastic wave device 31 has the acoustic reflection film 37, the energy of the elastic wave can be effectively confined to the piezoelectric layer 6 side.
　本実施形態における圧電性基板３２上の電極構造は、第１の実施形態と同様である。よって、一対のエッジ領域において音速をより確実に低くすることができ、ピストンモードをより確実に成立させることができる。従って、横モードをより確実に抑制することができる。 The electrode structure on the piezoelectric substrate 32 in this embodiment is the same as that in the first embodiment. Therefore, the speed of sound can be more reliably lowered in the pair of edge regions, and the piston mode can be more reliably established. Therefore, the transverse mode can be suppressed more reliably.
１…弾性波装置
２…圧電性基板
３…支持基板
４…高音速膜
５…低音速膜
６…圧電体層
７…ＩＤＴ電極
８，９…反射器
１５Ａ，１５Ｂ…誘電体膜
１６…第１のバスバー
１７…第２のバスバー
１８…第１の電極指
１９…第２の電極指
２２Ａ～２２Ｄ…圧電性基板
２４…高音速支持基板
３１…弾性波装置
３２…圧電性基板
３４ａ，３４ｂ…高音響インピーダンス層
３５ａ，３５ｂ…低音響インピーダンス層
３７…音響反射膜
Ａ…交叉領域
Ｃ…中央領域
Ｅ１，Ｅ２…第１，第２のエッジ領域
Ｇ１，Ｇ２…第１，第２のギャップ領域 1 ... Elastic wave device 2 ... Piezoelectric substrate 3 ... Support substrate 4 ... High-pitched sound film 5 ... Low-pitched sound film 6 ... Piezoelectric layer 7 ... IDT electrodes 8, 9 ... Reflectors 15A, 15B ... Dielectric film 16 ... First Bus bar 17 ... Second bus bar 18 ... First electrode finger 19 ... Second electrode finger 22A to 22D ... Piezoelectric substrate 24 ... High sound velocity support substrate 31 ... Elastic wave device 32 ... Piezoelectric substrate 34a, 34b ... High Acoustic impedance layers 35a, 35b ... Low acoustic impedance layer 37 ... Acoustic reflection film A ... Crossing region C ... Central region E1, E2 ... First and second edge regions G1, G2 ... First and second gap regions

Claims (10)

  1. 　圧電性基板と、
    　前記圧電性基板上に設けられており、複数の電極指を有するＩＤＴ電極と、
    を備え、
    　前記ＩＤＴ電極の隣り合う電極指が弾性波伝搬方向において重なり合っている部分が交叉領域であり、前記交叉領域が、前記複数の電極指が延びる方向における中央側に位置している中央領域と、前記中央領域の前記複数の電極指が延びる方向両側に配置されている一対のエッジ領域と、を有し、
    　前記一対のエッジ領域において、前記圧電性基板と前記複数の電極指との間に設けられている誘電体膜をさらに備え、
    　前記誘電体膜が、酸化ハフニウム、酸化ニオブ、酸化タングステン及び酸化セリウムからなる群から選択された少なくとも１種の誘電体からなる、弾性波装置。     Piezoelectric substrate and
    An IDT electrode provided on the piezoelectric substrate and having a plurality of electrode fingers,
    With
    The portion where the adjacent electrode fingers of the IDT electrodes overlap in the elastic wave propagation direction is a crossing region, and the crossing region is a central region located on the central side in the direction in which the plurality of electrode fingers extend, and the above. It has a pair of edge regions, which are arranged on both sides of the central region in the direction in which the plurality of electrode fingers extend.
    In the pair of edge regions, a dielectric film provided between the piezoelectric substrate and the plurality of electrode fingers is further provided.
    An elastic wave device in which the dielectric film is made of at least one dielectric selected from the group consisting of hafnium oxide, niobium oxide, tungsten oxide and cerium oxide.
  2. 　圧電体層を有する圧電性基板と、
    　前記圧電性基板上に設けられており、複数の電極指を有するＩＤＴ電極と、
    を備え、
    　前記ＩＤＴ電極の隣り合う電極指が弾性波伝搬方向において重なり合っている部分が交叉領域であり、前記交叉領域が、前記複数の電極指が延びる方向における中央側に位置している中央領域と、前記中央領域の前記複数の電極指が延びる方向両側に配置されている一対のエッジ領域と、を有し、
    　前記一対のエッジ領域において、前記圧電性基板と前記複数の電極指との間に設けられている誘電体膜をさらに備え、
    　前記圧電体層がタンタル酸リチウム層であり、
    　前記ＩＤＴ電極が主電極層を有し、前記主電極層がＡｌ層であり、
    　前記ＩＤＴ電極の電極指ピッチにより規定される波長をλ［μｍ］、前記誘電体膜の厚みをｔ＿Ｄ［λ］、前記誘電体膜の誘電率をε、前記誘電体膜の密度をｄ［ｋｇ／ｍ３］、前記誘電体膜のヤング率をＹ［ＧＰａ］、前記圧電体層の厚みをｔ＿ＬＴ［λ］、前記ＩＤＴ電極の前記主電極層の厚みをｔ＿Ａｌ［λ］とし、前記中央領域における音速をＶｃ、前記一対のエッジ領域における音速をＶｅとしたときに、前記ｔ＿Ｄ［λ］、前記ε、前記ｄ［ｋｇ／ｍ３］、前記Ｙ［ＧＰａ］、前記ｔ＿ＬＴ［λ］及び前記ｔ＿Ａｌ［λ］が、下記の式１により導出されるＶｅ／Ｖｃが１未満となる値である、弾性波装置。
    Figure JPOXMLDOC01-appb-M000001
         A piezoelectric substrate having a piezoelectric layer and
    An IDT electrode provided on the piezoelectric substrate and having a plurality of electrode fingers,
    With
    The portion where the adjacent electrode fingers of the IDT electrodes overlap in the elastic wave propagation direction is a crossing region, and the crossing region is a central region located on the central side in the direction in which the plurality of electrode fingers extend, and the above. It has a pair of edge regions, which are arranged on both sides of the central region in the direction in which the plurality of electrode fingers extend.
    In the pair of edge regions, a dielectric film provided between the piezoelectric substrate and the plurality of electrode fingers is further provided.
    The piezoelectric layer is a lithium tantalate layer, and the piezoelectric layer is a lithium tantalate layer.
    The IDT electrode has a main electrode layer, and the main electrode layer is an Al layer.
    The wavelength defined by the electrode finger pitch of the IDT electrode is λ [μm], the thickness of the dielectric film is t_D [λ], the dielectric constant of the dielectric film is ε, and the density of the dielectric film is d [kg. / M 3 ], the Young ratio of the dielectric film is Y [GPa], the thickness of the piezoelectric layer is t_LT [λ], the thickness of the main electrode layer of the IDT electrode is t_Al [λ], and the central region. When the speed of sound in the above pair is Vc and the speed of sound in the pair of edge regions is Ve, the t_D [λ], the ε, the d [kg / m 3 ], the Y [GPa], the t_LT [λ], and the above. An elastic wave device in which t_Al [λ] is a value at which Ve / Vc derived by the following equation 1 is less than 1.
    Figure JPOXMLDOC01-appb-M000001
  3. 　前記一対のエッジ領域の、前記複数の電極指が延びる方向における外側に、一対の高音速領域が配置されており、
    　前記一対の高音速領域における音速が、前記中央領域における音速よりも高い、請求項１または２に記載の弾性波装置。     A pair of high sound velocity regions are arranged on the outside of the pair of edge regions in the direction in which the plurality of electrode fingers extend.
    The elastic wave device according to claim 1 or 2, wherein the sound velocity in the pair of high sound velocity regions is higher than the sound velocity in the central region.
  4. 　前記圧電性基板が圧電体層のみからなる圧電基板である、請求項１～３のいずれか１項に記載の弾性波装置。 The elastic wave device according to any one of claims 1 to 3, wherein the piezoelectric substrate is a piezoelectric substrate composed of only a piezoelectric layer.
  5. 　前記圧電性基板が、高音速材料層と、前記高音速材料層上に直接的または間接的に設けられている圧電体層と、を有し、
    　前記高音速材料層を伝搬するバルク波の音速が、前記圧電体層を伝搬する弾性波の音速よりも高い、請求項１～３のいずれか１項に記載の弾性波装置。     The piezoelectric substrate has a hypersonic material layer and a piezoelectric layer directly or indirectly provided on the hypersonic material layer.
    The elastic wave device according to any one of claims 1 to 3, wherein the sound velocity of the bulk wave propagating in the high sound velocity material layer is higher than the sound velocity of the elastic wave propagating in the piezoelectric layer.
  6. 　前記圧電性基板が、前記高音速材料層と前記圧電体層との間に設けられている、低音速膜を有し、
    　前記低音速膜を伝搬するバルク波の音速が、前記圧電体層を伝搬するバルク波の音速よりも低い、請求項５に記載の弾性波装置。     The piezoelectric substrate has a low sound velocity film provided between the high sound velocity material layer and the piezoelectric body layer.
    The elastic wave device according to claim 5, wherein the sound velocity of the bulk wave propagating in the low-pitched sound film is lower than the sound velocity of the bulk wave propagating in the piezoelectric layer.
  7. 　前記高音速材料層が高音速支持基板である、請求項５または６に記載の弾性波装置。 The elastic wave device according to claim 5 or 6, wherein the hypersonic material layer is a hypersonic support substrate.
  8. 　前記圧電性基板が支持基板を有し、
    　前記高音速材料層が、前記支持基板上に設けられている高音速膜である、請求項５または６に記載の弾性波装置。     The piezoelectric substrate has a support substrate and
    The elastic wave device according to claim 5 or 6, wherein the hypersonic material layer is a hypersonic film provided on the support substrate.
  9. 　前記圧電性基板が音響反射膜と、前記音響反射膜上に設けられている圧電体層と、を有し、
    　前記音響反射膜が、音響インピーダンスが相対的に高い高音響インピーダンス層と、音響インピーダンスが相対的に低い低音響インピーダンス層と、を有し、
    　前記高音響インピーダンス層と前記低音響インピーダンス層とが交互に積層されている、請求項１～３のいずれか１項に記載の弾性波装置。     The piezoelectric substrate has an acoustic reflection film and a piezoelectric layer provided on the acoustic reflection film.
    The acoustic reflection film has a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance.
    The elastic wave device according to any one of claims 1 to 3, wherein the high acoustic impedance layer and the low acoustic impedance layer are alternately laminated.
  10. 　前記圧電体層がタンタル酸リチウム層である、請求項４～９のいずれか１項に記載の弾性波装置。 The elastic wave device according to any one of claims 4 to 9, wherein the piezoelectric layer is a lithium tantalate layer.
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